1. Technical Field of the Invention
This invention relates to an active type magnetic bearing adapted to support a magnetic shaft rotatably.
2. Description of Prior Art
A magnetic bearing of the aforementioned type has been disclosed in U.S. Pat. No. 3,845,997 which was granted to Karl Boden, Nov. 5, 1974, and also in German Patent DE No. 2,213,465 also granted to Karl Boden. Although in the former, an attracting force created in the radial direction is controlled by superposing a magnetic field produced by a heteropolar electromagnet over a radial magnetic field (bias flux) produced by an annular permanent magnet, the construction of the magnetic path is not efficient. Likewise, in the German Patent is disclosed a construction having two sets of series connected coils wound around the circumference of a troidal magnetic core. However, the magnetic reluctance thereof becomes large and hence the efficiency of the magnetic field is not high.